Te Hapū o Ngāti Wheke Inc is the Papatipu Rūnanga legal entity that represents Ngāti Wheke, the hapū with manawhenua status over the Whakaraupō basin and surrounding areas as outlined in the Port Cooper Deed. This entire area is culturally significant to Ngāti Wheke and sustains the hapū. Te Hapū o Ngāti Wheke has a strategic plan, a key part of which is the protection and enhancement of the whenua, moana and awa. Ngāti Wheke hopes to be a part of the leadership in climate action for future generations.

Mō tātou, ā, mō kā uri ā muri ake nei.

For us and our children after us.

Christchurch City Council recognises the rangatiratanga of Ngāti Wheke over its whenua and is working in partnership to plan for impacts on public assets and places of value.

Low-lying coastal sections of Charteris Bay Road and Marine Drive are at risk from coastal hazards. These roads provide key access to Charteris Bay and through to Diamond Harbour, Purau and Koukourarata Port Levy, and are used by around 2,000 vehicles per day. They are part of a wider network of roads that connect communities across the Whakaraupō Lyttleton Harbour and Koukourarata Port Levy with each other and with the city. Some sections of these roads are protected with a rock wall, others are not. Water supply and wastewater pipes sit underneath the at-risk sections of these roads.

The Charteris Bay boat ramp is accessible from Marine Drive, where car parking and public toilet facilities are also available. Because of the relatively shallow water depth here, the boat ramp is mainly used during medium to high tides by recreational boaties.

At the head of Te Wharau Charteris Bay you can find tidal mudflats and inter-tidal zones that support a range of native salt-tolerant plant species. You can also find shellfish such as cockles, which are significant for their mahinga kai value. In some parts of the bay, the mudflats merge into a diverse saltmarsh ecosystem as the land rises. These ecosystems are nationally rare and threatened because humans have changed many of the natural environments they exist in. Together with the shingle fans that form around stream outlets across the bay, the saltmarsh provides important habitat for the estuarine birds and seabirds that feed and roost in the area.

There are small strips of beach throughout the bay that are well used by locals and visitors for swimming and seasonal recreation.

Coastal flooding, coastal erosion and rising groundwater all pose a risk to the southern end of Te Wharau Charteris Bay. The images below show that as sea levels rise, the area will experience deeper flood events and the public assets in the area will become more and more at risk. The floodwater will also stay around for longer as groundwater levels rise and it gets harder for surface water to drain away into the soil. Areas at risk of erosion are likely to lose land at a faster rate as sea levels rise.

It’s important to note that while we have a good understanding of how coastal hazards will impact us, it’s hard to predict the rate at which sea levels are going to rise further in the future. The rate of change will depend on global greenhouse gas emissions and what impact this has on our climate. If different tipping points are reached, it’s possible we’ll see sea levels rise much quicker. That’s why it’s important to have a plan in place for the future of our coastal communities.

Charteris Bay Road, Marine Drive, the underlying wastewater and water supply pipes, and the boat ramp are all at risk from coastal hazards. If nothing is done, rising sea levels will cause more and more road interruptions and closures, making it harder to travel to and through the area. Erosion of these roads will also have an impact on the water and wastewater pipes beneath them that service local households. Rising sea levels will result in increased coastal flooding and erosion of the local boat ramp.

The Coastal Panel has considered the workable options that would address the risks to each of these assets. These options are set out in the section titled ‘Adaptation pathways’.

Sometimes the way we decide to manage one asset will have an impact on how the other assets could be affected by coastal hazards and the options we have available to manage those risks. In Te Wharau Charteris Bay, the decision to protect the roads in their current location or to move them out of the hazard zone will have an impact on other assets.

1. Hold the line

We could flood-proof and protect the at-risk sections of the road in their current location for several decades. This option could be used to buy a bit more time or a lot more time, depending on how much is invested. A decision could then be made to switch to a ‘work with nature’ approach and move away from coastal hazards.

Over the long term, holding the line would likely involve improving and extending the rock armouring along Marine Drive, widening and raising the at-risk sections of road above future flood levels, and improving the ability for stormwater to drain away. The protection of the road would also provide protection for the underlying pipes. However, over time, the beaches and inter-tidal mudflats would be lost as sea levels rise to meet this hard edge.

Protecting Marine Drive in its current location would also protect the existing access to the boat ramp, parking area and public toilet facilities. This area could be armoured to stop the land being lost to erosion over time. The boat ramp itself may need to be raised at some point in the future to ensure it’s useable.

2. Work with nature

In time, it may be better to move at-risk sections of both Charteris Bay Road and/or Marine Drive away from the shorefront and out of the hazard zone, creating a new way to access Te Wharau Charteris Bay and connect with the surrounding communities. This option could be used when it becomes too hard and expensive to maintain the existing road, or when actions to protect it (‘hold the line’) become less effective.

Moving the road wouldn’t necessarily mean moving the underlying pipes at the same time, although this is an option. They could be left in place until the risk of erosion becomes too great.

Moving these sections of road would provide some space for the mudflats, beach and existing foreshore to move inland as sea levels rise, meaning they’d continue to provide recreational and ecological benefits.

Access to the boat ramp may change or be lost if at-risk sections of Marine Drive were moved away from the coastal hazard zone. Because the boat ramp itself is also at risk, at some point in time we’d need to consider closing and removing it.

Both of these approaches come with their own opportunities, risks and costs, and they may need to be used at different times or could be more appropriate for some assets than others. Regardless of what we do, it’s going to get harder, more expensive and environmentally disruptive to keep public assets in this area, particularly near the shorefront where coastal erosion, flooding and groundwater all pose a risk.

Maintaining the at-risk sections of Charteris Bay Road and Marine Drive is expected to become harder and more expensive over time. The adaptation pathway map below shows that at a certain point – likely around 5 to 20 years from now – changing conditions will mean a new approach is needed to avoid increasing costs and disruption. As we near this point, we could look to flood-proof and protect the roads to different levels to buy us a bit more time or a lot more time. Alternatively, we could move the roads straight away or wait until a point in time when flood-proofing and protection isn’t working as well, and then move them. Some sections of the roads are likely to need work sooner than others.

*We don’t yet have enough information to understand exactly what the cost of this option would be.

The wastewater and water supply pipes are resilient to groundwater and flooding impacts because of the materials they’re made of, but they’re at risk from coastal erosion. The adaptation pathway map below shows that at a certain point – likely around 10 to 25 years from now – increasing erosion will mean action is needed to avoid damaging these pipes. The pipes are underneath the road, so a decision to protect the road would also mean the pipes were protected. If the road was moved, the pipes could be moved at the same time or left in place until the risk of erosion became too great.

*We don’t yet have enough information to understand exactly what the cost of this option would be.

The pathway map below shows that at a certain point in time – likely around 10 to 25 years from now – sea-level rise will mean the boat ramp is no longer useable. Over this timeframe, decisions about managing the risk to the road will likely also affect how the boat ramp, parking area and public toilet can be accessed. If there’s long-term access to the area, the boat ramp can be flood-proofed by raising it above future sea and flood levels, and the surrounding land protected against erosion. Closing and potentially removing the boat ramp would need to be considered if there was no long-term access to the area, or at a point in time when flood-proofing and protection became less effective.

*We don’t yet have enough information to understand exactly what the cost of this option would be.